1. Field of the Invention
The present invention is directed to a composite sheet material, useful as a component for asphalt shingles, which provides improved tensile strength.
2. Description of the Prior Art
High strength, uniform thin sheets or mats of glass fibers have become very important in the building materials industry. Probably the best example of the use of this type of material is in roofing shingles. The art is replete with descriptions of glass fiber mats and methods of making those mats having improved strength characteristics formed of glass fibers and made commercially by a wet-laid process.
For example, an interesting description of the development of this process is set forth in U.S. Pat. No. 4,135,029. Glass fiber mats made by the wet-laid process are formed by combining glass fibers held together by a binder material. Although binders useful in this application include urea-formaldehyde resins, phenolic resins, bone glue, polyvinyl alcohols, acrylic resins and polyvinyl acetates, urea-formaldehyde resins are preferred due to their low cost.
Conventionally, wet process glass fiber mats are made from glass fiber held together by a binder, which may comprise a thermosetting polymer system. Typically, the binder is applied in a liquid form and dispersed onto the glass fibers by a curtain type applicator. Conventional wet processes strive to produce a uniform coating of binder on the glass fibers. After the binder and glass fibers have been dried and cured, the glass fiber mat is then cut as desired.
A major problem in the manufacture and use of glass fiber mats resides in inadequate tensile strength. Inadequate tensile strength causes interruption in roofing manufacture. Equally important, inadequate tensile strength reduces the ability of the finished roofing to resist stresses in service on a roof.
The prior art has addressed this problem in the manufacture and use of glass fiber mats. For example, U.S. Pat. No. 4,430,158 provides improved tensile strength to a sized glass fiber mat by adding an anionic surfactant which contains hydrophobic segments containing from 8 to 30 carbon atoms and anionic segments which may be carboxy, sulfate ester, phosphate ester, sulfonic acid and phosphonic acid.
A further means of increasing the tensile strength of glass fiber mats, disclosed in U.S. Pat. No. 5,865,003, involves the application of high and low concentrations of a binder. A certain application is utilized to apply the binder to the glass mat, where the excess binder is removed using a vacuum.
Yet a further means of improving tensile strength of glass fiber mats employed as roofing shingles is taught in U.S. Pat. No. 4,542,068 which discloses a method of making a glass fiber mat in which an alkoxylated alkylamine having the formula
is added to a binder composition which comprises urea-formaldehyde and in which glass fibers are dispersed in a wet-laid process.
The prior art includes several disclosures that mention acrylonitrile-butadiene-styrene for use in applications which are of interest in relation to the present invention.
U.S. Pat. No. 5,095,055 describes the improvement of storage stability of acid treated polymer modified asphalts. Although the disclosure applies only to asphalts that are modified to enhance rheological properties, the '055 patent recites that such stability is important in applications that include roofing. The modifying agent is a branched polymer. Although a multiplicity of branched thermoplastic polymers are recited in the '055 patent, one of them is a copolymer of acrylonitrile-butadiene-styrene. It is emphasized that no disclosure of use of this polymer as a modifier of glass fiber mat binders is made.
U.S. Pat. Nos. 4,513,045 and 4,543,158 disclose a sheet type felt which primarily comprise cellulosic fibers but also include glass fibers, a binder and asphalt. The felt is recited to be useful as siding, roofing underlayment or as a facer for foamed insulation boards. Of interest is the inclusion of an acrylonitrile-butadiene-styrene copolymer, among many other foamable polymers, in the formation of rigid foamed insulation boards.
U.S. Pat. No. 3,919,356 concerns flame retardant polymeric compositions. In that disclosure acrylonitrile-butadiene-styrene resins, among several others, are employed with a class of compounds, referred in the '356 patent as CNB. Among the materials rendered flame retardant by the addition of the flame retardant compositions of the '356 patent is asphalt.
U.S. Pat. No. 6,030,559 sets forth a method of continuously manufacturing a plastic foam, which may be an acrylonitrile-butadiene-styrene copolymer, reinforced by a fibrous material.
The above remarks establishes the need in the art for a new composite glass fiber mat sheet having improved tensile strength as well improved tensile strength products which utilize those glass fiber mat sheets, such as roofing products, including shingles and roll roofing.